1. Field of the Invention
The present invention relates generally to the field of fuel cells, and in particular to a modularized separate plate structure for forming a fuel cell stack.
2. Description of the Prior Art
Fuel cell power system is capable of generating electrical power energy by means of electrochemical reaction between a fuel, such as hydrogen and methanol, and an oxidizer, such as oxygen. The fuel cell is classified, based on the electrolyte thereof, as proton exchange membrane fuel cell or polymer electrolyte membrane fuel cell, abbreviated as PEMFC or PEM, alkaline fuel cell (AFC), phosphoric acid fuel cell (PAFC), molten carbonate fuel cell (MCFC) and solid oxide fuel cell (SOFC).
Among these known fuel cells, the PEMFC is the best-developed technique, having the advantages of low operation temperature, fast start-up and high power density. Thus, the PEMFC is very suitable for transportation vehicles and power generation systems, such as home power systems and other portable and stationary power generation systems.
The fuel cell generates electrical energy through electrochemical reaction of hydrogen and oxygen, with water as by-product. Basically, the electrochemical reaction occurred in the fuel cell stack is a reverse reaction of electrolysis of water, in which chemical energy is transferred into electrical energy. The fuel cell comprises anode and cathode plates separated from each other with electrolyte arranged between and in physical contact with both the anode and the cathode. A circuit 20 is also incorporated in the fuel cell for conduction of the electricity out of the fuel cell. A typical structure of the fuel cell is shown in FIG. 1 of the attached drawings, comprising an anode plate 10 and a cathode plate 14 opposite to and spaced from each other with electrolyte 18 provided therebetween. A catalyst 12 is provided at the anode plate 10. When hydrogen is conducted to the anode plate 10 and catalyzed by the catalyst 12 the following reaction is carried out at the anode:H2→2H++2e−
The hydrogen ions produced at the anode 10 migrate through the electrolyte 18 and reach the cathode plate 14. Meanwhile, oxygen is conducted to the cathode 14 in which a catalyst 16 is provided. With the catalysis of the catalyst 16, oxygen undergoes the following reaction with hydrogen ions at the cathode:½O2+2H++2e−→H2Owith water as reaction product.
Besides water, the electrochemical reaction also generates heat. To prevent the fuel cell from overheating and maintain it at high performance, a cooling means is commonly employed in the modularized fuel cell stack in order to properly and timely remove heat from the fuel cell stack. An example of the cooling means is a cooling plate structure that is incorporated in a fuel cell to remove heat therefrom. Water, air and the likes can be employed as coolant that circulates through the cooling plate for heat removal.
To optimize the operation efficiency of a particular fuel cell, the anode plate and the cathode plate, as well as the cooling plate, must be configured so that gases, including hydrogen, oxygen and air, are allowed to flow through the plates in a substantially uniform manner. In designing the plates, the following factors are critical and should be considered: (1) the uniform flowing of gases through all the channels formed inside each plate, (2) the consistency of the length of channels for even distribution of gases, (3) the maximal and uniform contact of gases with the catalysts in each channel for undergoing electrochemical reaction in the channel and (4) the flow rates of gases for maintaining the electrochemical reaction that is sufficient to supply the desired amount of electricity. Besides, in case of the cooling plate, sufficiency and efficiency in removing heat is another factor to be taken into account.